1. Field of the Invention
The present invention relates to a method for hydrogen production using a rotating packed bed, especially to a method using a rotating packed bed having a single channel or multiple channels and providing high gravity field by rotating. Under suitable operation conditions, said method enhances the mass transportation and the reaction thereof in order to achieve efficient production of hydrogen.
2. Description of the Prior Art
A traditional packed bed tower is a common separation device used in chemistry industry in contacting procedures between gaseous and liquid phases, such as distillation, absorption, desorption or air-stripping. Commonly, the packed bed tower is built as a large cylinder up to several meters in height. The packed bed tower is equipped therein with a large amount of packing material for increasing contact area between gaseous and liquid phases. Since the mass transportation between the gaseous and liquid phases are driven merely by the gravity, this leads to slow progressing of liquid membrane, small contact area, low mass transportation factor as well as the necessity of employing a packed bed of large volume for achieving a required separation efficiency. A separation process carried out with the traditional packed bed tower consumes more energy and costs more on facilities and space requirements. It is thus apparent that traditional packed bed towers need to be improved to raise separation efficiency, lower energy consumption and reduce space occupied.
When the foregoing traditional packed bed tower is in use, besides the characteristics of mass transportation and the flows, density and viscosity of interchanging fluids, the characteristics of the packing materials, packing conformation, specific surface area, porosity and gravitational acceleration also affect the process.
Traditional practices adjust the characters of the fluids, the characters of the packing materials and conditions for operating the fluids to reduce the possibility of overflow. Contrary to the traditional practices, an increase in gravitational acceleration in the packed bed may effectively reduce the possibility of overflow and lead to higher separation efficiencies. Thus high gravitational rotating packed bed is employed. Generally, a conventional practice uses a high gravitational field generated by rotation to decrease the occurrence of overflow and allow larger scale airflow operations, or in other words, larger through put. Furthermore, accelerated gaseous-liquid backflows in turn shorten the time for reaching a balance between the gaseous and liquid phases and allow a better mixing level that increases effective contact area between the gas-liquid and the packing materials, which also provides thinner liquid membranes formed in the pores, an increased mass transportation factor as well as increased separation efficiencies. The high gravitational rotating packed bed has various advantages, especially small size, high efficiency, low energy consumption, short retaining time and large through put and thus may be widely used in process including steps of mass transportation controlling, for example, distillation, absorption, desorption, air-stripping or gaseous-liquid reaction with diffusion control. The high gravitational rotating packed bed may also drastically reduce space necessary for a plant compared with plants that use the traditional packed bed tower.
On the other hand, the abusing of fossil fuel since the industrial revolution not only reduces the reserve thereof but also keeps increasingly destroying the ecological environment. Recently, large amount of carbon dioxide released to and accumulated in the atmosphere has caused serious greenhouse effect and global warming resulting in abnormalities of global climate. Being aware of the issues involving environmental protection, including stopping global warming and mitigating greenhouse effect, which are recognized by the international community as a crucial matter, developed countries are urged to seek alternative and renewable energies, in order to cease releasing carbon dioxide, the unpleasant side-product of nonrenewable energies.
Alternative and renewable energies in research include: solar energy (photoelectrical and thermal energy), wind power, hydroelectric power, biomass energy (biomass diesel fuel, biomass alcohol and marsh gas), ocean energy and hydrogen power. Among the foregoing energies, hydrogen power is specifically discussed for its cleanliness, purity, transportability, energy density and sustainability and thus known as a “green energy.” Available methods for hydrogen production include: 1) thermochemical methods, 2) electrochemical methods, 3) photoelectric methods and 4) bioelectrical methods. Currently, the primary practical methods for hydrogen production are thermochemical and include: steam reforming, partial oxidation, autothermal reforming, gasification, water gas shift reaction and pyrolysis.
Among the aforementioned thermochemical methods for hydrogen production, the water gas shift reaction allows a carbon monoxide gas or a mixture of carbon monoxide gas and hydrogen gas, i.e., a syngas, to react with steam with catalyst to obtain hydrogen from steam, wherein the carbon monoxide is turned to carbon dioxide. A conventional reactor for hydrogen production provides thermal energy by burning or with electricity. Recent research provides a microwave reactor that uses microwave radiation to initiate water gas shift reaction and methanol vapor reforming, and also a Swiss roll reactor that uses thermal circulation and thermorecycling to produce hydrogen at an improved efficiency, demonstrating the research value and practical value of developing new reactors for hydrogen production.
The high gravitational rotating packed bed generates a high gravitational field in the rotating packed bed by means of centrifugation. The reagents in said high gravitational field is highly separated in order to increase contact area as well as the collision probability between the reagents, so as to achieve rapid mixing and reaction. As set forth above, the packed bed is widely used for distillation, absorption, desorption, air-stripping or gaseous-liquid reaction with diffusion control. However, the aforementioned processes are carried out with low-temperature gaseous-liquid systems whose operating temperatures are often at room temperature and are not practical under high-temperature gaseous conditions or applicable in a hydrogen production process. Hydrogen energy development is a promising industry. Application of high gravitational rotating packed bed in hydrogen production is expected to feature large through put, reduced space requirement, high mass transportation rate, low energy consumption and low cost, revealing characteristics of a device and technology with vast potential.
Furthermore, the aforementioned rotating packed bed is filled with catalysts so as to form a complete ring. Such structure requires large amounts of catalysts and drastically raises the cost when expensive catalysts are used.
To overcome the shortcomings, the present invention provides a method for hydrogen production to mitigate or obviate the aforementioned problems.